Conventionally, as an ultraviolet light source that generates ultraviolet light, an electron beam-excited ultraviolet light source is known, and for the ultraviolet light source, for example, Al2O3 doped with Sc (also described as “Sc:Al2O3”) is used as a light-emitting material.
BinLi et al., “Ultraviolet emission and Fano resonance in doped nano-alumina”, JOURNAL OF APPLIED PHYSICS 101, 053534 (2007), studies the relationship between the crystal structure of Al2O3 in Sc:Al2O3 and CL (Cathode Luminescence) intensity, and discloses that when firing is performed at high temperature (for example, about 1200° C.), the crystal structure of Al2O3 changes from the δ phase and the θ phase to the α phase to increase the proportion of the α phase, and thus the CL intensity increases. In other words, the literature discloses that good CL intensity is obtained by the fact that crystalline Sc:Al2O3 has a predetermined crystal structure (α-Al2O3). An ultraviolet light-emitting material using Sc:Al2O3 is also disclosed in Japanese Unexamined Patent Publication No. 2013-245292.